It’s Still Flu Season, So Here’s a Guide to Decoding Your Snot

Like plenty of other things, mucus is fine in moderation. In fact, it’s essential to our day-to-day functioning, keeping the throat from becoming too dry and moistening the air making its way to the lungs. It also acts as a first line of defense against any foreign substances trying to invade the body through the nose: The stickiness bogs particles down before they can make any progress, and the snot itself is full of germ-fighting substances.

That snot overload you experience when you’re sick, in other words, is actually a good thing — it means your body’s upping its defenses against whatever virus or bacteria has made its way in. In fact, as a recent video from the American Chemical Society explains, the way your snot looks can actually tell you a lot about what’s going on inside your body, like a sort of built-in color-coding system.

The default state is clear — when you’re healthy, anything you blow out your nose should be fairly colorless. When it starts to take on a new hue, though, it’s a sign that something’s up: “Yellow or white mucus turns up when you’re congested,” the video explains, “and a higher concentration of living and dead white blood cells have thickened the discharge.” (Even when you avoid using the word “snot,” it seems, there’s no non-disgusting way to talk about it.) And green means your immune system has sent in the big guns: white blood cells called neutrophils. The green color comes from an enzyme called myeloperoxidase, a substance produced by the neutrophils to help them carry out their infection-destroying mission.

And finally, there’s red mucus: It isn’t a sign of illness, but it is a sign that your finger’s spent enough time up there to cause bleeding, so maybe ease up a little bit.

Beyond the color, paying attention to your mucus can clue you in to which type of treatment can help you cope with an overabundance of it: If your snot’s wedged up in your sinuses, causing the kind of congestion that makes it hard to breathe properly, go for a decongestant, which cuts down on swelling in the nasal passages to ease that feeling of pressure. If it’s running all over the place, on the other hand, your best bet might be an antihistamine; true to its name, the drug counteracts histamine, the chemical that helps your body to create more mucus.

Or alternatively, you could do nothing. Research on the effectiveness of cold medicine has yielded some iffy results — the best thing to do may be just rest up and wait it out in snotty misery. If nothing else, it gives you a prime opportunity to take a snelfie or two.